Island, where there is increased runoff and recharge from large runway and tarmac surface areas devoid of vegetation, does the lens water remain fresh. Thus, the amount of potable ground water is not only dependent on the geolog: of the island and the amount of annual rainfall, but also the density of vegetation on the island. With the current stand of vegetation on Bikini Island, a very heavy rainfall, or lighter rainfall occurring with short time intervals between rainfall episodes, is required to produce a flow through to the lens. The total annual rainfall] and the rate at which it is delivered is very important to the level of recharge of the lens in a given year. For example, the rainfall of 77 inches in 1986 was the highest in several years and the groundwater salinity decreased as a result; however, the salinities in the various wells were still, for the most part, high enough to render the water unpotable. REMEDIAL MEASURES Based on the current concentrations of !3/Cs in vegetation and soil on Bikini Island and our current diet model, it will take about 80 to 90 y for radiological decay of '37Cs to reduce the !37Cs concentrations to a level that the estimated radiological dose to residents from all exposure pathways would be below current Federal guidelines. As a result, we have been evaluating several potential methods for reducing the amount of !37cs in the soil column and/or blocking the transfer of '37cs from soil to plants. In general terms, the methods can be classified as follows: 1}. Excavation. 2. Chemical competition. 3. Matrix immobilization. 4. Repeated cropping of vegetation. Some of these options have been evaluated and rejected. For example, repeated cropping of vegetation that contains !'3/cCs, and its subsequent disposal, to reduce the !3/Cs content of the soil is not a reasonable solution. The limited fresh water supply at the Atoll eliminates any consideration of irrigation on an island-wide basis, thus limiting the choice 70